Houston reservoirs release water amid 'thousand-year' flood

Water was released Monday from two Houston reservoirs to relieve pressure on structures designed for "a thousand-year flood," as an unprecedented storm displaced thousands in the rain-soaked American city (AFP Photo/JOE RAEDLE)

Chicago (AFP) - Water was released Monday from two Houston reservoirs to relieve pressure on structures designed for "a thousand-year flood," as an unprecedented storm displaced thousands in the rain-soaked American city.

Engineers said the reservoirs were filling up at a rate of six inches per hour, faster than water could be drawn out by normal use, as the powerful storm Harvey pummeled Texas for the third day.

Concerned that water could overtop the structures, flooding nearby homes, engineers instead opened release valves into a nearby river.

"We are doing controlled releases from both dams to minimize the volume of uncontrolled releases," Lars Zetterstrom of the US Army Corps of Engineers told CNN.

Still, officials warned some homes would inevitably flood as waterways feeding into the reservoirs continued to swell after more than two feet (60 centimeters) of rain fell in the region over a 24-hour period.

Both dams under pressure were designed to hold back unprecedented amounts of rain, meaning the current storm was "more than a thousand-year flood event," Zetterstrom said.

"You have to release some water right now to keep the level steady," he said.

The number of people needing shelter was expected to swell, as overwhelmed rescuers and citizen volunteers continued to pluck people from flooded homes and roadways.

"People who may not have been in a crisis state yesterday may find themselves in a crisis state today," Houston Mayor Sylvester Turner said, adding that 5,500 people were already in city shelters.

Forecasters warned that Harvey will regain strength and inundate the Gulf shore again by Wednesday.

At least three people have died so far, in what the National Hurricane Center called the biggest rainstorm on record.